Answer:
D. increasing the number of mitochondria
Explanation:
The mitochondria are membrane-bound cellular organelles found in the cell of an eukaryote. Mitochondrion is responsible for the production of energy since the process which releases the energy (cellular respiration) occurs in it.
In an experimental procedure whereby the amount of energy which is produced by a cell is about to be increased will involve the increase of the number of mitochondria in that cell. Since more mitochondria means more energy production.